1. Field of the Invention
The present invention relates to a SCARA-type robot structure and to a SCARA-type robot provided with such a structure.
2. Brief Description of the Related Art
In the conventional way, a robot of the SCARA, or “Selective Compliance Assembly Robot Arm” type, first of all comprises a fixed base structure able, for example, to be placed on a bench. It is also provided with an arm that can move with respect to the base structure, at least in terms of rotation, especially about a vertical axis.
Finally, this robot is equipped with a member, such as a flange, able to accept a tool, for example a gripper or a grinding tool. This tool accepting member is able to move with respect to the aforementioned arm. Thus, it may first of all be mounted directly on this arm, with the possibility of rotating.
By way of alternative, the tool accepting member may be mounted on an auxiliary arm, which is itself free to rotate with respect to the first arm. In the latter instance, the tool accepting member may be fixed, or alternatively able to move, with respect to the auxiliary arm. Finally, the tool accepting member is designed to be able to move in terms of translation with respect to the base structure, usually along a vertical axis.
SCARA robots, which perform well in terms of speed, repeatability and accuracy, are used in many industrial operations such as loading and unloading, or alternatively component assembly. This type of robot is also advantageous, over other technologies, in that it lends itself well to learning operations. Such operations consist in leading the robot's tool accepting member by hand to a desired location, then storing this configuration in memory, rather than programming it in.
To make this manipulation easier and safer it is necessary, initially, with a view to carrying out this learning operation, to block the translational movement of the tool accepting member, while at the same time allowing the first arm, and the auxiliary arm assuming that there is one, to rotate. Next, the tool accepting member is unblocked in terms of translational movement, allowing this tool to be placed in the appropriate position, and logged.
EP-A-1 525 957 discloses a SCARA-type robot which comprises a base structure, a first arm that is able to move with respect to this base structure only in terms of rotation, and a second arm, mounted on the aforementioned first arm and free only in terms of rotation with respect to the latter. Finally, there is a shaft, which acts as the tool accepting member, mounted on the second arm. This shaft is able to move with respect to this arm both in terms of rotation and in terms of translation, under the action of two motors housed in this second arm.
This known solution does, however, display certain disadvantages associated in particular with its sizable bulk. Thus, the presence of the two motors within the second arm, which are placed one above the other, means that this second arm is extremely bulky, along a vertical axis. Furthermore, the tool accepting shaft mounted on this second arm necessarily projects with respect to the latter, along this same axis. Finally, it is necessary to take account of the travel of this shaft in this vertical direction.
These various reasons mean that the robot described in EP-A-1 525 957 is of appreciable bulk, at least in terms of the second arm that bears the tool, in the vertical direction. This is disadvantageous in as much as it prevents this SCARA robot from being integrated into a work zone to which access is tight, for example under a press, thus considerably reducing the multifunctionality of such a robot.
Furthermore, in the arrangement described in EP-A-1 525 957, the collection of wires which electrically and pneumatically power the tool and the motors positioned in the arms, extends from the base structure towards the second arm, on the outside of the covers surrounding the latter. This collection of wires, also known as a wiring harness, therefore suffers significant torsion during the various movements of the robot, this considerably weakening the aforementioned electrical members.
This wiring harness which is protected only by a sheath, is soon damaged, in so far as it is subject to pulling, premature wear as the robot moves, and potential for deterioration when the robot is positioned in aggressive working environments, for example in corrosive or dust-laden environments. Furthermore, having a wiring harness outside the cover is disadvantageous in terms of bulk, because the position of the harness varies according to the movements of the robot which means that the overall bulk of the robot is liable to vary at random.
Finally, it will be noted that the second arm is equipped with three motors, together with their associated drive lines. This means that this second arm has a necessity to have a large volume, and high inertia, something which is disadvantageous in terms of performance.
Another source, U.S. Pat. No. 6,199,444 discloses a SCARA-type robot which comprises a base structure and a pillar mounted such that it can move, only in terms of translation, with respect to this base structure. To this end, this structure is provided with a screw-nut system to provide for such translational movement.
Furthermore, a first arm is mounted such that it can move in terms of rotation with respect to this pillar, while there is a second arm, able to move in rotation with respect to this first arm, this second arm itself being provided with a tool accepting member mounted such that it can rotate.
This alternative solution to a certain extent solves the problem of bulk associated with the teachings of EP-A-1 525 957. Specifically, given that the translational movement of the tool is provided by the movable pillar, this tool and its accepting member occupy only a small amount of space in the axial direction, indeed markedly less space than is inherent in the device of EP-A-1 525 957.
However, U.S. Pat. No. 6,199,444 does not provide any solution regarding the presence of the power supply wiring harness. Indeed, in the teachings of that document, this wiring harness runs between the base structure and the first arm on the outside of the protective cover.
In addition, the robot described in this American patent is unable to cover a large working area. This is because the presence of the movable pillar means that the rotation of the first arm is soon restricted by the presence of the base structure which means that the robot does not enjoy large-amplitude movements.
Finally, SCARA-type robots described for example in JP-A-61 293691, EP-A-1 646 455 and US-A-2005/193854 are known. These robots call upon a hollow member through which the abovementioned wiring harness partially runs.
The teachings of these documents therefore make it possible, to a certain extent, to solve the problem associated with the power supply wiring harness. By contrast, the solution that they describe presents disadvantages associated with the high number of mechanical components needed for setting the robot arms in motion, this being accompanied by high inertia in movement and a substantial bulk.